This invention relates to measuring the temperature of fluids in a pipe. Refrigeration and air conditioning technicians need temperatures of fluids in pipes for proper adjustment. If they can get the temperature of the pipe itself, in most cases that's good enough.
Many companies supply products that include various mechanisms and technologies to get the temperature of the pipe. These include beaded thermocouples with a Velcro strap, thermistors in a ‘clothespin’ style clamp, and several different methods of using thermocouples in a plastic clamp.
There are primarily two thermocouple techniques used for pipe clamps. One is to weld the individual thermocouples to a metal plate, and then mechanically press the metal plate against the pipe. The thermocouple delivers a voltage proportional to somewhere between that delivered by the two junctions to the plate.
To accommodate a wider variety of pipes, the plate has to be “V” or “U” shaped. If the plate is a “V,” at best there are two line-shaped contacts. Most of the contacting force for big pipes is on one plate, while the contacting force for the little pipe is on the other plate, with the varying force creating thermal conducting problems, since conductivity varies with the force applied.
Beyond that, the impediments to speed and accuracy with this technique are many, including that the plate dissipates heat to the environment easily due to big area of contact with ambient air. The contact point with the plate may be far from the thermocouple junctions; the contact spot changes as the jaws of the clamp get wider; the contact spot size may be small; the plate may absorb a lot of heat; the force between the contact plate and the pipe vary causing varying thermal conductance and the plate mounting mechanism (usually tabs) offers a path for heat to the environment. In addition, with any kind of clamp that has pivoting arms (like scissors or salad grabbers) the angle of the jaws vary as the clamp opens and closes, causing contact spot variability.
The other technique is to push a thermocouple junction made of ribbons of thermocouple material up against the pipe directly. This solves most of the problems of the plate, but is less rugged and more costly.